The present invention relates in general to an improved hard disk drive, and in particular to an improved pivot assembly for a hard disk drive actuator. Still more particularly, the present invention relates to a damped tolerance ring for the pivot assembly of a hard disk drive actuator to improve performance of the drive.
Generally, a digital data storage system consists of one or more storage devices that store data on storage media such as magnetic or optical data storage disks. In magnetic disk storage systems, a storage device is called a hard disk drive (HDD), which includes one or more hard disks and an HDD controller to manage local operations concerning the disks. Hard disks are rigid platters, typically made of aluminum alloy or a mixture of glass and ceramic, covered with a magnetic coating. Typically, several platters are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).
Within most drives, one read/write head is associated with each side of each platter and flies just above or below the platter""s surface. Each read/write head is connected to a semi-rigid arm apparatus which supports the entire head flying unit. More than one of such arms may be utilized together to form a single armature unit. Each read/write head scans the hard disk platter surface during a xe2x80x9creadxe2x80x9d or xe2x80x9cwritexe2x80x9d operation. The head/arm assembly is moved utilizing an actuator having an actuator body mounted on a pivot assembly. The actuator is often a voice coil motor (VCM) having a stator that is mounted to a base plate or casting. The base casting is also the foundation for a rotatable spindle that supports the disks. The base casting is mounted to a frame via a compliant suspension. When current is fed to the motor, the VCM develops force or torque which is substantially proportional to the applied current. As the read/write head nears the desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop directly over the desired track.
Modern HDD throughput and storage capacity have been substantially increased by improvement in actuator design which has resulted in increased precision and speed in head placement. The more precisely the actuator can place the read/write head, the greater the track density of the drive. However, rotary actuators have structural resonance modes that can affect disk drive performance. Some structural modes apply a reaction force against the pivot bearing, thereby tilting or rocking the actuator body on the pivot. Angular displacements of less than a milliradian of actuator rocking will cause the heads of the drive to go off-track. In the prior art, a number of solutions have been attempted to compensate for structural modes. For example, in U.S. Pat. Nos. 5,914,837 and 5,666,242, a set of O-rings provide some external vibration isolation and damping between the actuator body and the pivot. However, the small dimensions of the O-rings provide insufficient compressive force to give the system adequate stiffness to completely overcome the mode-induced forces. This O-ring design is incapable of providing sufficient stiffness for high track density disk drives. Although a much larger O-ring would provide more stiffness, it would force either the pivot groove or the bore to be greatly enlarged, thereby making insertion of the pivot into the actuator body much more difficult. In addition, geometric constraints on the parts limit the degree to which they may be scaled to larger dimensions.
Alternatively, a harder material could be used in the O-ring to provide greater stiffness, but this option would be less compressible, thereby also making insertion difficult. Moreover, compressed O-rings undergo stress relaxation when exposed to the elevated temperatures of disk drives over time, thereby diminishing any compressive force they may supply (i.e., the O-ring would flatten out into the groove and surrounding gap). In summary, this is not a good application for an O-ring since it must provide both damping/isolation and act as a spring.
When the O-rings are incorporated internally within the pivot assembly, the pivot assembly must be segregated into two portions that are screwed together. Problems with this design include forcing changes to the internal geometry of the pivot with thinner, less stiff ball bearings. In addition, the O-rings themselves must have a smaller diameter and, consequently, less stiffness to overcome the structural mode forces.
In U.S. Pat. No. 5,727,882, the pivot is bonded or glued with circular adhesive beads within the actuator body. This design provides no net compressive force between the pivot and the actuator body. Thus, the glued assembly is not sufficiently stiff to prevent an actuator from rocking against the pivot. Moreover, this design is not reworkable since the body is permanently joined to the pivot. Thus, an improved interface for disk drive pivots and actuators is needed.
All objects, features, and advantages of the present invention will become apparent in the following detailed written description.
A damped tolerance ring assembly has an outer tolerance ring, an inner tolerance ring, and an elastomeric layer bonded therebetween. In the illustrative embodiment, the tolerance rings are metal, spring-like split rings. Each tolerance ring has corrugations for additional strength. The elastomeric layer contours to the shape of both the inner and outer rings and their corrugations. The damped tolerance ring assembly is press fit between a cylindrical pivot assembly and a cylindrical hole in the actuator body of a disk drive. The friction at the interfaces of the tolerance rings due to compressive forces hold the pivot securely in the actuator body such that they all rotate together relative to a pivot shaft.
The tolerance rings are formed from steel and provide a stiff outer shell for the ring assembly to resist axial rocking of the actuator body relative to the pivot, especially during structural resonance modes. The thin layer of elastomer provides the damping and isolation to absorb vibration energy of the bearing reaction force. The vibration energy is not transferred to the read/write heads of the drive. Thus, track misregistration is reduced and performance is improved.
Accordingly, it is an object of the present invention to provide an improved hard disk drive.
It is an additional object of the present invention to provide an improved pivot assembly for a hard disk drive actuator.
Still another object of the present invention is to provide a damped tolerance ring for the pivot assembly of a hard disk drive actuator to improve performance of the drive.